1. Field of the Invention
This invention relates to an improved process for making sulfonated lignin surfactants and their use as dispersants for dyestuff. More particularly, this invention relates to improving the fiber staining properties of a sulfonated lignin dye dispersant by controlling the amount of free-phenolic hydroxyl groups and the molecular weight.
Dyestuff compositions comprise, for the most part, a dye cake, i.e., disperse dyes and vat dyes, and a dispersant. These dyestuff compositions are widely used to color both natural and synthetic fibers. In the dyestuff composition, the dispersant serves three basic functions. It assists in reducing the dye particle to a fine size; it maintains a dispersing medium; and it is used as an inexpensive diluent. Generally, however, the dye dispersants are of two major types, sulfonated lignins from the wood pulping industry and naphthalene sulfonates from the petroleum industry.
2. The Prior Art
Unique characteristics of sulfonated lignins as dispersants are identified with their good compatibility to many dye systems, their outstanding dispersant characteristics at ambient and elevated temperatures and their availability. By no means are sulfonated lignins perfect dye dispersants. They are highly chromophoric and adsorptive in nature towards most fibers and contains reducing functions. Foaming characteristics, high pH and high ash content also add to the undesirable properties of some sulfonated lignins for use as surfactants.
A major problem associated with the use of sulfonated lignin dye dispersants is their tendency to stain the fibers, which is dependent upon the color of the dispersant, the chemical structure of the fiber and the chemical structure of the sulfonated lignin itself. Wool and nylon fibers are most susceptible to sulfonated lignin adsorption. These fibers possess a large number of amide structures capable of forming strong hydrogen bonds, especially with electron donating structures, such as acetic, phenolic and carboxylic acid groups. At acidic pH's, the various salts are beginning to be converted into their acids; and thus additional staining is seen. Sulfonated lignin absorbed to the fiber generally results in loss of brightness and in extreme cases, particularly with the lighter color shades, may cause intolerable color distortions.
A second detrimental effect caused by the action of sulfonated lignins as dispersants are their ability to reduce dyes of a di-azoid nature. Elimination of the double bond by hydrogenation will eliminate the color body of the particular dye and thus results in a colorless component. Therefore, the use of sulfonated lignins generally requires quantities of dyes greater than the theoretical requirements to compensate for potential color losses during the operation.
The same groups in lignin which permit adsorption onto the fiber are responsible for the good dispersing behavior. Blocking of these functions has for that reason resulted in products with less than desirable dispersibility, particularly at elevated temperatures. Blocking, which eliminates the most strongly reducing groups, such as phenols and catechols, has been used in eliminating or at least minimizing fiber staining and diazo dye reduction tendencies. One such method for reacting sulfonated lignin with epichlorohydrin is U.S. Pat. No. 3,672,817 to Falkehag et al. who teach an epichlorohydrin modified lignin as a dye dispersant. The process of this invention provides an improvement over the Falkehag et al. material.
Other reactants are available to modify lignins to improve certain properties, for example, dispersing ability, or to inhibit a property that is undesirable for certain uses, for instance, the undesirable dark color of lignin. By way of illustration of methods of modifying lignins, the following patents are cited. U.S. Pat. No. 3,600,308 to G. G. Allen describes reacting lignin with a variety of chemical agents to increase molecular weight for use as coagulants. U.S. Pat. No. 3,546,199 to D. T. Christian et al. describes a process for producing polyols from lignin. U.S. Pat. No. 2,854,444 to L. T. Monson et al. describes a process for oxyalkylating lignin sulfonic acid for use as wetting agents and dispersants. Additional examples of reacting or modifying lignin to make them more suitable as dye dispersants include U.S. Pat. No. 3,156,520 to L. A. Baisdell; U.S. Pat. No. 3,094,515 to K. F. Keirstead et al.; U.S. Pat. No. 3,726,850 to Detroit; U.S. Pat. No. 2,680,113 to E. Adler et al.; and U.S. Pat. No. 3,769,272 to Hintz. The art cited is meant to show the state of the art and is not intended to be all inclusive of lignin modifications.
Although the methods for treating sulfonated lignins described above offer some advantage during dyeing, none have produced a product possessing the improvements obtained by the products made according to the claimed process.
Thus, it is the general object of this invention to provide a process whereby sulfonated lignins or lignosulfonates may be treated to improve their usefulness as dye dispersants.
Another object of this invention is to provide a process whereby an epihalohydrin is used to both block a portion of the free-phenolic hydroxyl groups of the lignin and to sufficiently cross-link lignin molecules to increase molecular weight thereby providing a more heat stable dispersant while still leaving enough phenolic hydroxyl groups to interact with the dye particle.
Other objects, features and advantages of this invention will be seen in the following detailed description of the invention taken in conjunction with the accompanying drawings.